Baca, Alicia I.
Brown, Joseph J.
Bertness, Kris A.
Bright, Victor M.
Effects of design and materials on the dielectrophoretic self-assembly of individual gallium nitride nanowires (GaN NWs) onto microfabricated electrodes have been experimentally investigated. The use of TiO2 surface coating generated by atomic layer deposition (ALD) improves dielectrophoretic assembly yield of individual GaN nanowires on microfabricated structures by as much as 67%. With a titanium dioxide coating, individual nanowires were placed across suspended electrode pairs in 46% of tests (147 out of 320 total), versus 28% of tests (88 out of 320 total tests) that used uncoated GaN NWs. An additional result from these tests was that suspending the electrodes 2: 75 mu m above the substrate corresponded with up to 15.8% improvement in overall assembly yield over that of electrodes fabricated directly on the substrate.
Piezoelectric semiconductors such as GaAs are of interest for signal processing devices due to the possibility of monolithic integration of surface-acoustic-wave (SAW) -based devices and active electronic circuits on the same substrate. The common crystal orientation of GaAs for these applications has been the {100} cut. In this paper the characteristics of surface wave propagation in the {110} plane of GaAs, which supports both the Rayleigh and the Bleustein-Gulyaev surface wave modes, are investigated. Several test devices have been fabricated and studied using laser probe and S-parameter measurement techniques. The SAW velocity, attenuation, piezoelectric coupling constant, slowness surface, beam profile, and the transducer characteristics have been measured, and the experimental results agree well with the theoretical calculations for both types of the surface wave modes.
Herrmann, Cari F.
DelRio, Frank W.
Miller, David C.
George, Steven M.
Bright, Victor M.
Ebel, Jack L.
Strawser, Richard E.
Cortez, Rebecca
Leedy, Kevin D.
Atomic layer deposition (ALD) was used to deposit an alternative dielectric barrier layer for use in radio frequency microelectromechanical systems (rf MEMS). The layer is an alloy mixture of Al2O3 and ZnO and is proposed for use as charge dissipative layers in which the dielectric constant is significant enough to provide a large down-state capacitance while the resistivity is sufficiently low to promote the dissipation of trapped charges. This paper investigates Al2O3/ZnO ALD alloys deposited at 100 and 177 degrees C and compares their material properties. Auger electron spectroscopy was used to determine the Zn concentrations in the alloy films, which was lower than expected. Atomic force microscopy images revealed an average surface roughness of 0.27 nm that was independent of deposition temperature and film composition. The dielectric constants of the Al2O3/ZnO ALD alloys films were calculated to be similar to pure Al2O3 ALD, being similar to 7. Indentation was used to ascertain the modulus and hardness of the ALD films. Both the modulus and hardness were found to increase for the greater deposition temperature. ALD-coated rf MEMS switches showed a low insertion loss, similar to 0.35 dB, and a high isolation, 55 dB at 14 GHz. Mechanical actuation of the ALD-coated devices showed lifetimes of over 1 billion cycles. (c) 2006 Elsevier B.V. All rights reserved.
Bleustein-Gulyaev (BG) piezoelectric surface-wave propagation under a periodic metal-strip grating on piezoelectric cubic crystals is investigated. A general theory that fits both the elastic and electric periodic boundary conditions has been developed and is applicable to a grating with an arbitrary electrical connection between adjacent metal strips. Numerical examples are given for aluminum- and gold-shorted gratings on a gallium arsenide substrate. It is found that the BG waves which penetrate deep into the substrate in the absence of the metal grating become trapped at the surface when the grating is present. It is noted that the penetration depth is heavily dependent on the metal thickness. The relevant physical attributes of the wave such as particle displacement, electric potential, and dispersion are also computed and analyzed.
Ever since John Perry's developments in the late 70s, it is customary among philosophers to take de se contents as essentially tied to the explanation of action. The target explanation appeals to a subject-specific notion of de se content capable of capturing behavioural differences in central cases. But a subject-specific de se content leads us, I argue, to a subject-specific notion of intentional action that prevents basic forms of generalisation. Although this might be seen as a welcome revision of our pre-theoretical conceptions, I propose, instead, a strategy to circumvent this rather unexpected result: to reject subject-specific de se contents in favour of subject-specific ways of thinking that do not enter into the content of one's attitudes.
Hirano, Teruyuki
Dai, Fei
Livingston, John H.
Fujii, Yuka
Cochran, William D.
Endl, Michael
Gandolfi, Davide
Redfield, Seth
Winn, Joshua N.
Guenther, Eike W.
Prieto-Arranz, Jorge
Albrecht, Simon
Barragan, Oscar
Cabrera, Juan
Cauley, P. Wilson
Csizmadia, Szilard
Deeg, Hans
Eigmueller, Philipp
Erikson, Anders
Fridlund, Malcolm
Fukui, Akihiko
Grziwa, Sascha
Hatzes, Artie P.
Korth, Judith
Narita, Norio
Nespral, David
Niraula, Prajwal
Nowak, Grzegorz
Paetzold, Martin
Palle, Enric
Persson, Carina M.
Rauer, Heike
Ribas, Ignasi
Smith, Alexis M. S.
Van Eylen, Vincent
We report on the discovery of three transiting super-Earths around K2-155 (EPIC 210897587), a relatively bright early M dwarf (V =3D 12.81 mag) observed during Campaign 13 of the NASA K2 mission. To characterize the system and validate the planet candidates, we conducted speckle imaging and high-dispersion optical spectroscopy, including radial velocity measurements. Based on the K2 light curve and the spectroscopic characterization of the host star, the planet sizes and orbital periods are 1.55(-0.17)(+0.20) R-circle plus and 6.34365 +/- 0.00028 days for the inner planet; 1.95(-0.22)(+0.27) R-circle plus and 13.85402 +/- 0.00088 days for the middle planet; and 1.64(-0.17)(+0.18) R-circle plus and 40.6835 +/- 0.0031 days for the outer planet. The outer planet (K2-155d) is near the habitable zone, with an insolation 1.67 +/- 0.38 times that of the Earth. The planet's radius falls within the range between that of smaller rocky planets and larger gas-rich planets. To assess the habitability of this planet, we present a series of three-dimensional global climate simulations, assuming that K2-155d is tidally locked and has an Earth-like composition and atmosphere. We find that the planet can maintain a moderate surface temperature if the insolation proves to be smaller than similar to 1.5 times that of the Earth. Doppler mass measurements, transit spectroscopy, and other follow-up observations should be rewarding, as K2-155 is one of the optically brightest M dwarfs known to harbor transiting planets.
Frith, J.
Pinfield, D. J.
Jones, H. R. A.
Barnes, J. R.
Pavlenko, Y.
Martin, E. L.
Brown, C.
Kuznetsov, M. K.
Marocco, F.
Tata, R.
Cappetta, M.
Using the Position and Proper Motion Extended-L (PPMXL) catalogue, we have used optical and near-infrared colour cuts together with a reduced proper motion cut to find bright M dwarfs for future exoplanet transit studies. PPMXL's low proper motion uncertainties allow us to probe down to smaller proper motions than previous similar studies. We have combined unique objects found with this method to that of previous work to produce 8479 K < 9 M dwarfs. Low-resolution spectroscopy was obtained of a sample of the objects found using this selection method to gain statistics on their spectral type and physical properties. Results show a spectral-type range of K7-M4V. This catalogue is the most complete collection of K < 9 M dwarfs currently available and is made available here.
Aberasturi, M.
Caballero, J. A.
Montesinos, B.
Gálvez-Ortiz, M. C.
Solano, E.
Martín, E. L.
Using Virtual Observatory tools, we cross-matched the Carlsberg Meridian 14 and the 2MASS Point Source catalogs to select candidate nearby bright M dwarfs distributed over similar to 25,000 deg(2). Here, we present reconnaissance low-resolution optical spectra for 27 candidates that were observed with the Intermediate Dispersion Spectrograph at the 2.5 m Isaac Newton Telescope (R approximate to 1600). We derived spectral types from a new spectral index, R, which measures the ratio of fluxes at 7485-7015 angstrom and 7120-7150 angstrom. We also used VOSA, a Virtual Observatory tool for spectral energy distribution fitting, to derive effective temperatures and surface gravities for each candidate. The resulting 27 targets were M dwarfs brighter than J = 10.5 mag, 16 of which were completely new in the Northern hemisphere and 7 of which were located at less than 15 pc. For all of them, we also measured H alpha and Na I pseudo-equivalent widths, determined photometric distances, and identified the most active stars. The targets with the weakest sodium absorption, namely, J0422+2439 (with X-ray and strong Ha emissions), J0435+2523, and J0439+2333, are new members in the young Taurus-Auriga star-forming region based on proper motion, spatial distribution, and location in the color-magnitude diagram, which reopens the discussion on the deficit of M2-4 Taurus stars. Finally, based on proper motion diagrams, we report on a new wide M dwarf binary system in the field, LSPM J0326+3929EW.